Regarding a non-destructive inspection technique, an ultrasonic inspection is known.
An ultrasonic inspection technique is disclosed in Patent Literature 1 (JP H09-133664A). Patent Literature 1 discloses covering an inspection surface of an inspection object with waveguide substance whose acoustic impedance value is equal to or approximate to that of the inspection object so that the inspection surface of the non-inspection object becomes flat. Also, Patent Literature 1 discloses that a waveguide is removed from the inspection object and attached to another inspection object (reference to para. 0021).